Admittance function to evaluate aerodynamic loads on vehicles: Experimental data and numerical model

When a moving vehicle is subjected to cross wind, the aerodynamic loads acting on the vehicle itself depend not only on the mean value of the relative wind-vehicle velocity but also on the statistical properties of the wind, i.e. the turbulence intensity – which represents its variation in the time domain – and the integral length scale – linked to the space distribution of the wind field. This paper describes an algorithm, used to define non-stationary aerodynamic forces, which allows to account for the spatial correlation of the wind through the aerodynamic admittance function. In particular, a numerical model for the aerodynamic admittance function is developed and verified by means of comparison with experimental data. The model can be adopted for both the lateral force and rolling moment components but not for the vertical force. Finally, it will be shown how admittance depends on the geometrical characteristics of the vehicle (length and height) and on the properties of the wind, through the integral length scale.     

基于LabVIEW的惯性测量单元信号采集及处理系统设计

利用LabVIEW设计了惯性测量单元信号采集及处理软件,主要包括串口通信、数据分离及信号处理等模块;串口通信模块采用VISA方式编程,建立了惯性测量单元与上位机之间的通信;根据惯性测量单元输出数据的格式,利用LabVIEW中的匹配模式函数分离出沿三轴向的加速度信号和角速率信号;设计了一种用于去除加速度信号中低频成份的数字滤波器;在建立的陀螺漂移模型基础上,分别进行小波基、小波分解层数、阈值函数及阈值估计方法等小波参数的选取.     

Mechanism of resonance and cancellation for train-induced vibrations on bridges with elastic bearings

In this paper, the mechanism involved in the phenomena of resonance and cancellation in the train-induced vibrations of railway bridges with elastic bearings is explained using an analytical approach. The train is modelled as a sequence of moving loads of constant intervals. The vibration shape of the elastically supported beam is approximated by the combination of a flexural sine mode and a rigid body mode. The present results indicate that under certain conditions, resonances of much higher peaks can be excited on elastically supported beams by moving trains at much lower speeds than those on simply supported beams. The cancellation is a phenomenon more decisive than that of resonance, in that it can suppress the latter even when the condition of resonance is met. Moreover, the speed for cancellation to occur is generally independent of the support stiffness. To verify the analytical results presented herein, a field test was conducted on two adjacent elastically supported bridges in existing railway lines. In the design of railway bridges, it is important that the phenomenon of resonance not be overlooked, as it is harmful not only to the riding comfort of passengers, but to the maintenance of railway tracks.     

有限多类别交通网络的扩展Wardrop均衡

研究有容量约束的交通网络中有限多类别用户的扩展Wardrop均衡.证明扩展Wardrop均衡定义的4种等价形式;并利用凸集分离定理得到在一定条件下.定义中A(v)的存在性.A(v)可以看作是一种收费,因而得到了有限多类别的交通网络中收费的存在性.     

Wave forces on a submerged horizontal plate - Part I: Theory and modelling

This paper is concerned with the propagation of nonlinear gravity waves over a thin horizontal plate submerged in water of shallow depth. An unsteady solution of the problem is obtained by use of the theory of directed fluid-sheets for the two-dimensional motion of an incompressible and inviscid fluid. Particular attention is paid to the calculation of the nonlinear wave-induced vertical and horizontal forces and overturning moment by solving the Level I Green–Naghdi equations. The theoretical formulation of the problem is given in this paper (Part I), while the results due to solitary and cnoidal waves, and comparisons with the available experimental data are given in a companion paper under the same title (Part II).     

一种数字全息图零级项消除的新方法

针对离轴数字全息图中的零级项问题,提出用独立分量分析方法对零级项进行压缩.首先通过CCD获取同一物体的两幅干涉强度不同的全息图构成观测信号,然后采用独立分量分析方法(Independent Component Analysis(ICA))从观测信号中分离出零级项和共轭项,再从获得的共轭项中减去残余的零级项分量,实现零级项的有效压缩,并用模拟结果论证该方法在处理零级项压缩方面的优越性和有效性.     

由偏微支配的系统的最优控制理论中的奇异摄动方法*

本文介绍了由偏微分方程支配的系统的最优控制理论中有关应用奇异摄动方法时出现的各种问题。考虑了渐近分析来自状态方程。或来自性能指标函数,也考虑了状态方程是定义在摄动域内的情形。     

Completed and incompleted stochastic webs

In this paper,the completed stochastic web and incompleted stochastic web producedby the perturbed saddle separatrix net are given.The structural properties of two kinds ofweb are discussed by means of the dynamical system theory.     

基于激光扫描的接触网几何参数检测方法研究

针对当前电气化铁路接触网几何参数日常检测的需求,提出了一种基于激光扫描的接触网几何参数检测方法,即结合激光扫描仪、光电编码器和工控机等硬件设备进行编程处理以实现相关几何参数的非接触式采集、采样点定位和数据处理以获得接触网的各个几何参数,经试验该方法能有效的提高接触网几何参数检测精度,测量精度达到±3mm,具有实际意义。     

Kinematic hardening model suitable for ratchetting with steady-state

A new kinematic hardening model useful for simulating the steady-state in ratchetting is developed within the framework of the strain hardening and dynamic recovery format. The model is formulated to have two kinds of dynamic recovery terms, which operate at all times and only in a critical state, respectively. The model is examined on the basis of nonproportional experiments of Modified 9Cr–1Mo steel at 550°C and IN738LC at 850°C. The experiments include multiaxial, as well as uniaxial, ratchetting, multiaxial cyclic stress relaxation, and nonproportional cyclic straining along a butterfly-type strain path. It is shown that the model is successful in simulating the experiments, and that the model is featured by the capability of representing appropriately the steady-state in ratchetting under multiaxial and uniaxial cyclic loading.